This invention relates to telemetry of signals in a fluid system and more particularly relates to a method and apparatus for sending signals up a wellbore from a downhole unit in a logging-while-drilling system.
It has long been recognized that efficiency of drilling operations could be greatly improved if there were a system able to measure downhole drilling parameters and/or formation characteristics and transmit them to the surface during drilling operations, or with only momentary interruptions of the drilling operations.
Several such systems have been proposed and are commonly referred to as "logging-while-drilling" systems. In logging-while-drilling systems, one of the major problems exists in finding a means for telemetering the information concerning the desired parameter from a downhole location to the surface and have it arrive in a meaningful condition.
It has been proposed to telemeter the desired information by means of a continuous pressure-wave signal generated within the mud system normally associated with rotary drilling operations. The pressure wave signal which is representative of a particular parameter is generated in the mud near the bit by a generating means and the wave travels up the hole through the mud to a signal detector at the surface. Present systems, using circulating mud as a medium for telemetering, have obvious difficulties in that the normal mud pump pulsations and other extraneous vibrations, shocks, etc., of the drilling equipment give an unwanted pressure wave or noise to the mud which may seriously distort or mask the desired signal being transmitted in the mud at that time. It is to be noted that the present invention described herein concerns a method for transmitting signals uphole through the fluid in a manner to avoid most of the interferences associated with the previous systems. This will be explained in detail hereinafter.
There are many logging-while-drilling patents issued. Typical of those include: U.S. Pat. Nos. 3,742,443; 3,736,558; 3,302,457; 3,739,331; 3,736,558; 3,732,728; 3,737,843; and 3,727,179.